1. Field of the Invention
The present invention relates to a percussion electrical hand-held tool such as, e.g., hammer drill or chisel hammer, and in particular, to percussion electrical hand-held tool with a pneumatic percussion mechanism.
2. Description of the Prior Art
In percussion electrical hand-held tools, a rotational movement, which is generated by the electromotor of an electrical hand-held tool, is transformed, at least partially, by suitable transformation means, in an oscillating or percussion translational movement. Usually, wobbling oscillations are transformed into oscillations along an oscillation axis that is parallel to the drive shaft, and eccentric oscillations are transformed into oscillations along an axis extending transverse to the drive shaft. In most cases, the oscillation movement is transmitted in a pneumatic percussion mechanism via a driving piston to a gas spring, a percussion piston and, finally, to the working tool. In hammer drills, additionally, a rotational movement is transmitted, via a suitable gear unit, to the working tool spindle. In this case, the ratio of the oscillation frequency or the number of blows applied to the working tool to the rotational speed is maintained constant. Optionally, this ratio can be made discretely switchable from one value to another.
European Publication EP 759 341 discloses use in a hand-held tool of a free impact automatic action which provides, with the use of appropriate means, e.g., an axially displaceable switching sleeve that opens the valves of the percussion mechanism, for a discrete, optionally stepwise, interruption of impacts upon reduction of axial operational pressure applied to the working tool. In the disclosed tool, a constant control of the impact energy by a user is not possible.
Japanese Publication JP 414653/90 discloses use of a planetary gear unit for a stepwise change-over of the rotational speed of the working tool spindle. In the tool discloses in the Japanese Publication, a constant adjustment of the number of impacts in accordance with the rotational speed of the working tool spindle is not possible.
German Publication DE 35 05 544 discloses a hand-held tool in which the oscillation amplitude is constantly adjusted by adjusting an axial position of an eccentric, with the eccentricity being constantly changed by an inclined eccentric journal.
European Publication EP-063 725 discloses a hand-held tool in which a planetary gear unit is used for driving an eccentric journal. In this planetary gear unit, the dimension of the planetary gear and the sun gear, which has an inner toothing and within which the planetary gear is displaceable, are so selected that a rectilinear leg of trajectory follows each point on the pitch circle of the planetary gear. By rotating the sun gear 90xc2x0, the piston stroke can be changed from a full stroke, which corresponds to the pitch circle diameter of the sun gear, to almost zero. For a continuous adjustment of the amplitude of the oscillation or reciprocating movement, the sun gear is secured in a respective angular position with a self-locking worm gear unit or with a radially extending adjusting handle.
In the electrical hand-held tool, it is customary to continuously control the rotational speed by controlling the driving power with an electronic phase-controlling means arranged in the current feed circuit. The phase-controlling means is controlled with a finger-actuatable pressure knob arranged in the tool handle, dependent on the immersion depth of the knob. The rotational speed is controlled to provide for smooth start of the hand-held tool or for control of the rotational speed by the user.
German Publication DE 195 03 526 discloses a hand-held tool in which the tool handle is supported in a position transverse to the working tool axis and is rotatable relative thereto with a possibility of being offset relative thereto. This permits the use of the obtained limited degree of freedom along the working tool axis for damping of the vibrations.
The object of the present invention is to provide for continuous control by the user of the impact power in the hand-held tools independently of the rotational speed of the tool drive.
This and other objects of the present invention, which will become apparent hereinafter are achieved by providing a percussion electrical hand-held tool in which the amplitude of the reciprocating or percussion movement or impact amplitude is adjusted in accordance with a manual axial force applied to the tool handle.
Essentially, according to the present invention a planetary gear unit is used as crank gear unit. In the planetary gear unit, the dimensions of the planetary gear and the sun gear, which has an inner toothing and within which the planetary gear is displaceable, are so selected that a rectilinear leg of trajectory follows each point on the pitch circle of the planetary gear.
The eccentric journal of the planetary gear is connected by a connecting rod with impact-producing means, e.g. a percussion piston, that reciprocates parallel to the working tool axis. In this case, the angular position of the continuously adjustable sun gear depends on the force applied to the handle along the working tool axis.
As a result of a constant adjustment of the sun gear, the angle of the rectilinear reciprocating movement of the eccentric journal is likewise constantly adjusted. Thus, with respect to a predetermined rotational speed, the impact energy is constantly adjusted by adjusting the impact amplitude. This solution encompasses disconnection of the idle impact at the setting of the sun gear in the vicinity of zero.
The setting, i.e., the angular position, of the sun gear is effected with an adjustment mechanism mechanically, pneumatically, or electronically connected with the tool handle. The adjustment mechanism is formed as a self-locking mechanism so that the forces, which act. in a direction opposite the direction of action of the reciprocating movement generating forces, would act on the entire housing and not predominantly on the handle. The displacement region of the handle, which actually controls the impact power, lies in the range of up to 3 cm and provides for change of the sun gear setting up to xcfx80/2.
Advantageously, as an adjusting means, a self-locking, worm gear unit is used. The worm gear unit comprises a worm gear toothing provided on the outer circumference of the sun gear. The means, which includes a gear unit, for driving the worm gear unit are advantageously controlled by servo control means, using the power available in the hand-held tool. For adjusting the sun gear setting, an available kinetic drive power is used. The kinetic drive power is provided by the available pneumatic compression power or by a controllable adjusting motor driven by the electrical power available in the hand-held tool.
When a controllable adjusting motor is used, the impact power can be controlled by a user or a microcontroller according to desired operational characteristics. According to the invention, the actual impact power applied to the working is adjusted in accordance with the data obtained with displacement, pressure, and acceleration sensors to arrive at a set impact power.
The control of the set impact power by controlling the impact amplitude is effected, advantageously, independent from the control of the drive power with the pressure knob, by measuring the axial force applied to the handle of the hand-held tool, as this axial force innately corresponds to the wishes of the user. To this end, advantageously, the handle is axially displaced by a limited amount against an axial counterforce toward the working tool or the workpiece. Thereby, the setting of the sun gear is changed, increasing the percussion power.
Advantageously, the handle is secured to the tool housing, radially offset with respect to the working tool axis, with a hinge arranged transverse to the working tool axis. The axial force is measured indirectly, in accordance with the handle displacement, or directly by a piezo force sensor and communicated to the microcontroller as a set value. The microcontroller calculates the setting of the sun gear in accordance with a readable by the controller performance diagram in a form of a suitable non-linear mapping of the axial force or of the handle displacement. The calculated setting of the sun gear, which provides for the necessary impact power, is effected by an adjusting motor.
Advantageously, the calculation is effected in accordance with further suitable characteristic values such as rotational speed, torque, current and acceleration. Optionally, the tool type and size also can be taken into consideration for achieving an optimal and reliable operation in accordance with the readable by the controller, performance diagram.
However, the proper weight of the tool, the operational direction, and the gravity acceleration, which depends on its weight, can adversely affect the determination of the set value of the impact energy. To prevent the adverse effect of these factors, the operational direction is determined by a gradient sensor, and with the proper weight being known, the microcontroller calculates the true, desired set value of the impact power. To this end, the gradient sensor is connected with the microcontroller. The microcontroller corrects the real, measured axial force applied to the handle in accordance with a retaining force which corresponds to the proper weight of the hand-held tool multiply by the cosine of an angle formed by the operational direction of the tool and the direction of the gravity acceleration.
The novel features of the present invention, which are considered as characteristic for the invention, are set froth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.